Slovakia's government said Thursday the suspect in the shooting of Prime Minister Robert Fico was a lone wolf upset after a Fico ally won last month's presidential election.

"This is a lone wolf whose actions were accelerated after the presidential election since he was dissatisfied with its outcome," Interior Minister Matus Sutaj Estok told reporters. 

The gunman, arrested on the scene, is a 71-year-old writer. He was charged with the attempted murder on Thursday. 

Fico was in a stable but "very serious" on Thursday.

"He is able to speak but only a few sentences and then he is really, really tired... The situation is very critical," president-elect Peter Pellegrini told reporters outside the hospital. 

The shooting, which the government called a "political assault", stoked fears over heightened polarisation or even further violence just weeks before European parliament elections.

Slovakia's politics have been divided for years between pro-Europeans and nationalist-leaning camps, with the latest elections heavily influenced by disinformation, mutual accusations and attacks on social media.

"I am calling on all political parties in Slovakia to temporarily suspend or considerably reduce their European election campaign,"  Pellegrini told reporters.

Rescue workers wheel Slovak prime minister Robert Fico to a hospital after he was shot and seriously wounded. Photo: AFP

Pellegrini, Fico's ally who will assume office in June, said Slovakia should avoid "further confrontation" in a joint statement with the outgoing president Zuzana Caputova. 

Surgeons spent hours in the operating theatre, battling to save the 59-year-old leader after the shooting, which happened as Fico spoke to members of the public after a meeting.

Deputy prime minister Robert Kalinak said doctors stabilised Fico's condition, "but unfortunately, his condition is still very serious as the injuries are complicated." 

Fico is a contentious character in Slovakia. 

Since returning to office last October, Fico has made a string of remarks that have soured ties between Slovakia and neighbouring Ukraine.

He has questioned Ukraine's sovereignty and called for a compromise with Russia, which invaded in 2022.

After he was elected, Slovakia stopped sending weapons to Ukraine.